Samsung has built several different Galaxy S4 smartphones, including a U.S. version running a Snapdragon processor that requires an extra image processor to enable heavily promoted user functions such as eye-movement recognition.

IHS iSuppli, which conducted a teardown of the GS4, said Samsung sells a different model in South Korea that runs an eight-core Octacore Exynos 5 processor. The Octacore Exynos 5 chip costs $28, or $8 more than the Snapdragon, the market research firm said.

Unique eye-tracking capabilities in the GS4, such as a Smart Pause feature that can pause videos when a user looks away, have been heavily promoted by Samsung but have worked only sporadically for early users and reviewers.

"The Octacore Exynos 5 enables some unique, processor-intensive applications that are not possible with the Snapdragon processor," IHS iSuppli said in a statement released Thursday.

A Snapdragon processor by itself wouldn't allow the GS4 to fully support eye tracking. The addition of a Fujitsu image processor would be required to offload core processor functions.

Several features, including Smart Pause, were heavily promoted by Samsung executives when the GS4 was unveiled at Radio City Music Hall in New York City on March 14.

The IHS iSuppli teardown found that a U.S. GS4 model with 16 GB of flash memory includes $229 worth of materials. Samsung's cost rises to $237 when manufacturing costs are added. The materials used in a South Korean GS4 with 16 GB of memory costs $244 for materials, and $252 including manufacturing costs.

IHS iSuppli conducted a virtual teardown of the GS4 in March and found that a 16 GB U.S. LTE version was estimated to cost $233 for materials and rose by only $4 to $241 when manufacturing costs were added.

Vincent Leung, an analyst at IHS iSuppli, said that Samsung has built at least four different versions of the Galaxy S4 for different locations, including the U.S. and South Korea.

"Samsung is demonstrating its strategy of offering a mobile product that has appealing features and pricing -- and then adapting the device to suit the tastes of varying markets or regions," Leung said in a statement. "This approach is in stark contrast to the one-size-fit-all philosophy used by Apple, Samsung's primary competitor."

Leung noted that the South Korean and U.S. versions of the GS4 "look pretty much the same" and use many of the same core features, such as the enclosure, display, camera and battery.

In addition to different processors, the U.S. and South Korean versions include different wireless, sensor and interface, Wi-Fi, Bluetooth, FM radio and GPS subsystems.

Samsung manufactures the Octacore Exynos 5, which includes the "big-little" architecture created by ARM. The processor consists of four 1.6 GHz Cortex A 15 "big" cores and four 1.2 GHz Cortex-A7 "little" cores. The big cores handle high priority tasks while the little ones handle lower priority tasks.

The big-little architecture allows the South Korean version to process tasks quickly while retaining long battery life, IHS iSuppli said.

In an interview, Leung said that IHS iSuppli tested the two processors side-by-side, but not the the full eye tracking capabilities of the smartphones.

The Fujitsu image processor would add up to $5 to the cost of the U.S. version IHS iSuppli said.

The Octacore processor can most likely handles image processing related to eye tracking, Leung said, thus eliminating the need for a separate image processor. "We require further investigation of what this Fujitsu chip does," he said.

Leung said he could not fully explain eye-tracking consistency problems noticed by some critics in early reviews of the GS4, theorizing that Samsung's software, not the processing hardware, could be at fault.

In informal tests by Computerworld, the Smart Pause feature in a review U.S. GS4 smartphone only worked with certain videos, such as ones that were created on the device. The Computerworld test found that videos streamed from YouTube and other Web sites do not work with the U.S. version of the GS4.

A Samsung spokesman said that Smart Pause only works with self-produced videos and videos purchased from Samsung Hub.

Some GS4 reviewers, including Computerworld's JR Raphael, found that Smart Pause and some other unique Samsung software features worked inconsistently or, in some cases, not at all.

While praising some of the ideas behind the new eye-tracking features, Raphael found that they don't always work in darkened rooms. "Most of the Galaxy S4's software elements err on the side of gimmicky, with fleeting novelty but little lasting real-world value," he wrote.

Raphael was critical of Smart Pause, saying it only worked about 30% of the time. He also said that Smart Rotation (to adjust to a user's angle of height) didn't work at all.

Air Gestures -- the ability to move through Web pages with a wave of the hand -- and Air View, which is said to let users interact with content by hovering a finger over the screen, only worked inconsistently, Raphael found.